Flow direction in a centrifugal (radial) compressor Considering the machine geometry and blade motion, the primary flow of air through a centrifugal compressor is oriented in which direction relative to the rotor axis?

Introduction / Context:
Centrifugal compressors, also known as radial-flow compressors, transfer energy to the fluid by whirling it radially outward in a rotating impeller and then diffusing it in a stationary diffuser.

Given Data / Assumptions:

• Classic shrouded impeller and vaned or vaneless diffuser.
• Neglect minor inlet pre-swirl and exit blade lean effects.
• Axis refers to the shaft centerline.

Concept / Approach:
Fluid enters near the eye of the impeller and is flung outward by centrifugal action. Thus the main flow path is predominantly radial. A radial path is perpendicular to the machine axis, unlike axial compressors where flow is largely parallel to the axis.

Step-by-Step Solution:
Identify machine class: centrifugal (radial-flow).Track flow path: from impeller eye to impeller tip is radial.Relative to axis: radial = perpendicular to axis.Therefore, the correct orientation is perpendicular.

Verification / Alternative check:
Cross-sectional diagrams show streamlines moving outward from the centerline to the periphery before entering the diffuser.

Why Other Options Are Wrong:

• Parallel/inclined: describe axial or mixed-flow machines.
• “None of these” and “reverse to axis” do not match standard geometry.

Common Pitfalls:
Confusing compressor classes; “centrifugal” implies radial motion by definition.

Final Answer:
perpendicular